If you look at the line above, it tried to load first.js but failed with a 500 error (internal server error). If you try loading that first.js URL in your browser, you may see an error message explaining why, otherwise you'll have to do some more investigation in your web server logs.
General developer forum
Script error for "core/first"
Denne tråd er låst, så du kan ikke længere svare på den.